The present invention relates to a bulk erase device for carrying out magnetization, initialization, or annealing a recording film of an optical recording medium wherein embossed-pit rows with address information are zoned in the radical direction by laser irradiation, and relates to a preheating bulk erase device for an optical recording medium, a preheating bulk erase method for an optical recording medium, and an optical recording medium, wherein the temperature of the medium is increased by partial laser irradiation to the recording film while rotating the medium.
Conventionally, for optical recording media, the method called zoning is used for increasing the recording capacity by effective use of a recording area. This is a method of obtaining, on a medium rotating at constant angular velocity, for example, the recording density of a similar degree over the entire surface of the medium by switching a recording reference frequency for recording/reproducing for each radius.
By way of example, with ISO/IEC14517 (130 mm 4×), ISO/IEC15286 (130 mm 8×), ISO/IEC15041 (90 mm 5×) and the like, which are optical magnetic media of the ISO Standards, the recording capacity of the medium is increased by using this method.
Specifically, since a data recording/reproducing area is radially divided into a plurality of zones as shown in FIG. 1, and the recording/reproducing frequency is different for each zone, the number of sectors within a cycle varies. Thus, an address area shows a partially radial shape for each radius as illustrated by 1a. 
Moreover, with magneto-optical recording media, the medium is subjected to operation for uniformly arranging the magnetizing directions of a recording film before offering to users. Specifically, a greater magnetostatic field than a coercivity of the recording film is provided to the medium to perform operation for forcibly turning the magnetizing direction of the recording film to the erased direction, i.e. so-called magnetization.
Typically, when a recording film to be magnetized has a weak coercivity of the order of 0.8×106 A/m (A/m is an intensity of the magnetic field in SI unit), magnetization is possible by a weak magnetic field such as electromagnet. However, when magnetizing a recording film having a strong coercivity more than 1.19×106 to 1.59×106 A/m, the temperature of the recording film is increased to reduce the coercivity and apply a weak magnetostatic field less than 0.8×106 A/m so as to carry out magnetization.
With phase-change type media, the medium is subjected to operation for crystallizing the entire surface of a recording film before offering to users. Specifically, the recording film is heated/annealed by an amount more than a given amount to achieve initialization from a so-called Ad-depo state film wherein crystalline/amorphous exist in a mixed way after film formation to the totally crystallized state.
In this process of initialization, the recording film having a large area of some hundreds tracks is heated at a time to carry out magnetization and crystallization. This method is called bulk erase. Bulk erase is a method of heating a recording film by reducing in the radial direction of a medium a semiconductor laser of 1–2 W in an oval beam diameter having a major axis of more than 10 μm to provide only focusing on the recording film for irradiation to the rotating medium.
Bulk erase has not only an object of initialization of a recording layer, but also an effect (sensitivity shift) for reserving in advance the recording sensitivity or the reproducing sensitivity occurring at the time of repeated recording of a medium to control a sensitivity change during an user's medium service duration. It is considered that providing thermal energy to a recording film eases in advance atoms in an amorphous recording layer, thus obtaining stabilization of the recording film.
Parameters of bulk erase are the number of revolutions or linear velocity of a medium, radial feed pitch of a laser spot, laser power, laser beam width, and the like. Since these parameters can be controlled easily to allow stable occurrence of magnetization, initialization, and sensitivity shift, a very effective method is provided.
By carrying out tests on bulk erase of a magneto-optical recording medium in order to perform sensitivity shift and magnetization, the inventors of the present application have found the following problem. That is, after performing enough bulk erase for producing a predetermined sensitivity shift to the optical recording medium as shown in FIG. 1, which is radially zoned and has an address with embossed pit aligned radially in each zone, a tracking error is observed at a zone boundary. Then, the presence of a tracking-error increasing area was perceived as shown in a signal waveform diagram in FIG. 3.
FIG. 3 shows a relationship between an address signal and a tracking-error signal at a tenth track position from the zone boundary of the totally bulk-erased medium, wherein (a) shows an address signal, (b) shows a tracking-error signal, (c) shows an enlargement of an area F of the address signal (a), and (d) shows an enlargement of an area F of the tracking-error signal (b), respectively. In the Figure, E shows a track jump signal, G shows an enlarged address in the area F, and H shows a tracking-error increasing portion.
It is noted that the measuring conditions in FIG. 3 are linear velocity of 7.5 m/s, CLV, laser power of 1.5 mV, disc diameter of φ86 mm, measuring site of R40 mm, and application of tracking on a Land portion.
It is found that the tracking-error increasing portion H is not due to an influence of the address G, but has the same positional relationship with the address which existed in the zone of 10 tracks before. The address of as much as 10 tracks apart therefrom has some influence on a tracking error.
It is observed that the increasing amount of a tracking error in the tracking-error increasing portion H reaches 17% with respect to peak-to-peak amplitude of the track jump signal E, and that this phenomenon reaches some hundreds tracks out of the zone boundary. As a result, the drive (medium drive system) recognizes that those tracking-error increasing areas are defective areas, and carries out processing of replacement. Therefore, the medium has enormous replacement sectors.
The tracking-error increasing phenomenon as mentioned above does not occur when bulk erase is not performed. However, when bulk erase is not performed, the recording sensitivity varies during a period that an user uses a medium, and does not allow fulfillment of optimum recording/reproducing, causing an error.
It can be conceived to produce sensitivity shift according to a method of erasing record for each track by using a drive or the like, which requires, however, many times of erasing of record of the same track, taking a lot of time, providing no practical method.